Fabric development with nearest‐neighbor interaction and dynamic recrystallization

Abstract

[1] Polycrystals undergoing ductile deformation develop lattice-preferred orientation (fabric) as a result of intracrystalline slip. A consequence of fabric development is that bulk physical properties become anisotropic. Fabric development and macroscopic deformation are studied by examining three effects: nearest-neighbor interaction (NNI) among crystals, polygonization, and migration recrystallization. The effects of NNI are modeled by arranging the crystals on a three-dimensional cubic grid and assigning six neighbors to each crystal. The ''strength'' of interaction can vary from no interaction (homogeneous stress) to ''strong'' interaction (significant stress redistribution). Increasing the NNI leads to a more homogeneous strain. Fabric varies in both strength and symmetry at a given bulk strain, depending on the strength of NNI. For a prescribed fabric the strain rate increases as the NNI increases. Recrystallization is modeled from energy balance considerations, and polygonization is formulated in terms of stress differences. Both processes require knowledge of dislocation density, which is calculated in the model as a function of crystal strain and grain size, both of which vary with time. Models of fabric development in ice that include NNI lead to more realistic fabric evolution than models with homogeneous stress. However, available data on fabric evolution are inadequate to determine quantitatively the strength of NNI acting in ice.

The role of crystal fabric in flow near an ice divide

“…Azuma, 1994;Castelnau and others, 1996;Godert and Hutter, 1998;Gagliardini and Meyssonnier, 1999;Thorsteinsson, 2001Thorsteinsson, , 2002. Their approaches differ primarily in how they relate the stress applied to the ice aggregate to the local deformation rate of a crystal within the aggregate.…”

“…Because of these smaller predicted enhancements, T2001 and ModT2001 both underestimate the role of anisotropy. T2001 (and therefore also ModT2001) has two limitations; it does not predict the evolution of the fabric and it does not include interactions between neighboring crystals (Thorsteinsson, 2002).…”

“…Since ice in an ice sheet typically exhibits a strong non-random crystal fabric, and ice flow is dependent on orientation of crystals relative to the applied stress, we expect that a non-random crystal fabric might affect the flow field. For example, when basal planes are aligned parallel to the plane of maximum shear stress, deformation may be enhanced by a factor of 8 or 10 relative to that for isotropic ice (Budd and Jacka, 1989;Azuma, 1994;Azuma and Goto-Azuma, 1996;Castelnau and others, 1996;Thorsteinsson, 2002). Characterizing the flow pattern resulting from a non-linear flow law that also includes the effects of crystal fabric will improve predictions by ice-sheet flow models and interpretations of the divide signature.…”

Subgrain boundaries and related microstructural features in EDML (Antarctica) deep ice core

“…However, these depth ranges are usually not considered as discrete, but as overlapping, and some few grains can have the potential to initiate dynamic recrystallization at shallow depths (Thorsteinsson, 2002). The dominance of the three recrystallization regimes in a depth sequence for the majority of grains is currently widely accepted.…”

Ice crystal <i>c</i>-axis orientation and mean grain size measurements from the Dome Summit South ice core, Law Dome, East Antarctica

“…Lile, 1978;van der Veen and Whillans, 1994;Azuma and Goto-Azuma, 1996;Svendsen and Hutter, 1996;Thorsteinsson, 2002;Gillet-Chaulet et al, 2005;Placidi et al, 2010). In such flow relations the anisotropic viscosity of a polycrystalline aggregate is obtained from the orientation relationship between the grain c-axes and the stress configuration, or some parameterization of these orientation effects.…”